The present invention relates to a rear aperture converter and, more particularly, a rear aperture converter that compensates for changes in lens information due to its insertion.
In a photographic camera adapted to transmit lens aperture information for automatic exposure from the objective to the camera body by electric contacts arranged on a lens mount and a camera body mount, respectively, a change in said lens aperture information occurs due to insertion of a rear aperture converter. It is desirable to compensate for this change and to transmit the information compensated to the camera body without any special adjustment, although inserting the rear aperture converter between the objective and the camera body multiplies the effective aperture ratio.
When a rear aperture converter having a conversion ratio of 2 is used, the effective maximum aperture in F-value and minimum aperture in F-value are doubled with respect to the corresponding values peculiar to the objective itself, so that a direct transmission of aperture value signals from the objective to the camera body would make it impossible to achieve accurate exposure control and to display the effective aperture value associated with the automatic exposure. To solve this problem, a lever could be provided which is operatively associated with the diaphragm mechanism for regulation of the lens aperture value from the camera body; the lever would be displaced within the rear aperture converter by an amount corresponding to the change caused by the rear aperture converter. However, this would result in an extension of the range in which said lever operates and the mechanical displacement of the lever would lead not only to complication of the overall mechanism but also to low precision and reliability.